3通道煤粉燃烧器气固两相流动数值模拟

本文采用两相湍流流动的ｋ－ε－ｋｐ模型，对３通道煤粉燃烧器出口气流速度及煤粉浓度进行了模拟计算。     

旋风炉内气相燃烧及两相流动的数值模拟

在有反应两相流动及煤粉燃烧的全双流体模型（ＰＴＦ模型,ｐｕｒｅ ｔｗｏ－ｆｌｕｉｄ ｍｏｄｅｌ）基础上,采用修正的ｋ－ε－ｋｐ两相湍流模型,对旋风炉内的湍流气相燃烧（甲烷和一氧化碳的燃烧）及在气相燃烧条件下的两相流动进行了数值模拟研究,模拟结果表明,在有燃烧的情况下,在旋风炉的底部存在近壁回流区,该回流区有利于火焰稳定,气粒两相切向速度分布具有类似的Ｒａｎｋｉｎｅ涡结构,该研究为煤粉燃烧的数值模拟     

工业油水分离器湍流两相流场的数值模拟

本文应用双流体模型及ｋ－ε－ｋｐ两相湍流模型，研究了水力旋流器内油水两相湍流流场。建立了适用于旋流分离器中两种液体混合物的有旋湍流流动的ｋ－ε－ｋｐ模型。并针对影响旋流器分离效率的不同影响因素，进行了变更入口流动参数及分离器几何参数的数值实验，为工业用油水旋流分离器的优化设计提供了一个有效的数值模拟工具。     

煤粉复合旋流火焰燃烧特性研究（2）：数值模拟

本文数值模拟了煤粉旋流火焰燃烧过程，燃烧数值计算包括理论物理模型建立，数值方法两个大部分，计算模型处理了气相湍流与燃烧、气固两相流动、煤颗粒燃烧过程和辐射传热等物理化学过程，以ｋ－ε模型模拟湍流流动；ＰＤＦ法模拟气相扩散火焰燃烧；颗粒运动计算颗粒运动少颗粒湍流浓度方程模拟颗粒湍流扩散；通量法计算火焰辐射传热，煤粉颗粒复杂燃烧模型计算了颗粒尺寸、形状变化和颗粒孔隙内部燃烧、表面平度对整个颗粒的燃烧过程影响。计算获得了气相速度分布场、气相ｋ和ε分布场、气相温度场、气相组份场和颗粒浓度场及运动过程，揭示了煤粉复合旋流燃烧特性。     

不同湍流模型对强旋流动的数值模拟

在径向浓淡旋流煤粉燃烧器单相冷态试验的基础上，充分考虑旋转对湍流流场的影响，有用k-ε双方程及其修正模型和二阶矩雷诺应力模型（DSM），对流旋煤粉燃烧器出口强旋流场进行了数值模拟。数值计算结果表明：k-ε双方程模型定性上可以预报出强旋流场的主要特点，但回流区的预报区域偏大，轴向速度的预报结果与试验值有一定差距，预报的回流速度偏低，速度衰减过快，这是由于k-ε湍流模型采用了较多的简化和未考虑旋转对湍流的影响。采用基于旋转体系使湍流脉动加强和削弱两种作用的修正方法对k-ε双方程的湍流耗散率方程进行修正。计算结果表明：从旋转体系可使湍流能量加强出发的Bardina涡量修正方法，预报回流区范围较标准k-ε湍流模型缩小，更加接近于试验值。其计算结果优于使湍流 脉动削弱的Richardson修正。DSM模型对轴向回流速度和切向速度后期分布预报结果较上述模型有较大改善，可体现出湍流雷诺应力非均匀各向异性的特点，虽然此模型仍有收敛速度慢、计算时间长的缺点，但对预报强旋流动是一个精度较高、极具潜力的方法 。图9参11     

三维贴体坐标系下燃烧室中两相反应流的数值模拟

本文提供了现代航空发动机主燃烧室中三维两相燃烧流场的数值计算方法。气相场在欧拉坐标中用ＳＬＭＰＬＥ算法求解；液相场在拉格朗勒坐标系中用ＰＳＩＣ算法求解。本数值计算程序采用ｋ－ε双方程湍流模型，旋涡破裂湍流燃烧模型，六通量热辐射模型，采用了三维非正交曲线坐标系，压力交错网格。     

煤粉浓淡旋流燃烧器喷口气固两相流动的数值模拟

在实验基础上，运用PNG－ASM和FCFSRT模型对煤粉旋流浓淡燃烧器的气固两相流进行数值模拟，并与实验结果进行对比，得出了合理的颗粒速度场和浓度场；比较和计算了浓缩和未浓缩的颗粒场特性，说明了浓淡分离燃烧器的浓淡燃烧的机理；最后对浓淡分离燃烧器煤粉混合特性作了数值模拟，指出了煤粉浓淡混合的区域。     

旋流浓淡煤粉燃烧器出口区域冷态两相流场实验研究

采用三维相位多普勒颗粒分析仪（ＰＤＰＡ）对旋流浓淡煤粉燃烧器出口区域冷态两相流动特性进行了实验研究,获得了该燃烧器在不同旋流叶片开度、不同煤粉浓缩构件遮盖度、不同旋流二次风和直流二次风配比下的气固两相流场和浓度场的分布规律,并进行了讨论分析。     

速差射流煤粉燃烧器燃烧过程理论分析(Ⅰ)--强化燃烧原理分析

采用两相湍流流动的双流体模型 ,对带有中心高速射流的速差射流煤粉燃烧器进行了模拟计算。计算结果表明 ,燃烧器内筒端面与喷口间的距离 x有一最佳值 ,此时的高温回流量达到最大 ,煤粉燃烧的强化效果最好 ;另外 ,在该燃烧器中 ,中心高速射流能够浓缩煤粉 ,但约束煤粉扩展及增加高温烟气回流的作用不明显 ,只能使一次风粉与已回流的高温烟气混合更好 ,温度更均匀     

速差射流煤粉燃烧器燃烧过程理论分析——强化燃烧原理分析

采用两相湍流流动的双流体模型,对带有中心高速射流的速差射流煤粉燃烧器进行了模拟计算。计算结果表明,燃烧器内筒端面与喷口间的距离ｘ有一最佳值,此时的高温回流量达到最大,煤粉燃烧的强化效果最好;另外,在该燃烧器中,中心高速射流能够浓缩煤粉,但约束煤粉扩展及增加高温烟气回流的作用不明显,只能使一次风粉与已回流的高温烟气混合更好,温度更均匀。     

Numerical and experimental investigation of a mild combustion burner

An industrial burner operating in the MILD combustion regime through internal recirculation of exhaust gases has been characterized numerically. To develop a self-sufficient numerical model of the burner, two subroutines are coupled to the CFD solver to model the air preheater section and heat losses from the burner through radiation. The resulting model is validated against experimental data on species concentration and temperature. A 3-dimensional CFD model of the burner is compared to an axisymmetric model, which allows considerable computational saving, but neglects some important burner features such as the presence of recirculation windows. Errors associated with the axisymmetric model are evaluated and discussed, as well as possible simplified procedures for engineering purposes. Modifications of the burner geometry are investigated numerically and suggested in order to enhance its performances. Such modifications are aimed at improving exhaust gases recirculation which is driven by the inlet air jet momentum. The burner is found to produce only 30 ppm_v of NO when operating in MILD combustion mode. For the same air preheating the NO emissions would be of approximately 1000 ppm_v in flame combustion mode. It is also shown that the burner ensures more homogeneous temperature distribution in the outer surfaces with respect to flame operation, and this is attractive for burners used in furnaces devoted to materials' thermal treatment processes. The effect of air excess on the combustion regime is also discussed.     

锯齿形浓股出口结构下浓淡燃烧器出口区域的气固流场

应用颗粒动态分析仪测定了富集型煤粉燃烧器浓股出口加置锯齿型稳燃器前后的三维湍流速度场．试验结果表明,加置锯齿型稳燃器后,浓股气流在喷口附近的出口速度在三维方向上皆呈明显的波浪形分布,平均速度和脉动速度都有所增大,轴向平均速度衰减迅速,轴向脉动速度衰减延迟,水平径向和垂直径向的脉动明显增强．试验说明,锯齿型出口结构改善了喷口附近的气固流场,增大煤粉颗粒的局部空间浓度,增强气固混合,可以提高燃烧器着火稳燃和低NOx排放控制性能．     

Gas/particle flow and combustion characteristics and NOx emissions of a new swirl coal burner

Due to the limits of reserves and price for the high rank coal, the low rank coal has been employed as fuel for power generation in China and will be eventually employed in the world. To burn low rank coal, centrally fuel-rich swirl coal combustion burner has been studied in Harbin Institute of Technology. This paper reviews and analyzes the major research results. The work has included both experiments and numerical simulation. The experiments were conducted using small-scale single-phase experimental equipment, a gas/particle two-phase test facility and 200- and 300-MW_e wall-fired utility boilers. For the burner, the primary air and glass beads partially penetrate the central recirculation zone and are then deflected radially. At the center of the central recirculation zone, there is high particle volume flux and large particle size. For the burners the local mean CO concentrations, gas temperatures and temperature gradient are higher, and the mean concentrations of O₂ and NO_x in the jet flow direction in the burner region are lower. Moreover, the mean O₂ concentration is higher and the gas temperature and mean CO concentration are lower in the side wall region. Centrally fuel-rich burners have been successfully used in 200- and 300-MWe wall-fired pulverized coal utility boilers.     

Cold flow characteristics of a novel bluff body hydrogen burner

The cold flow characteristics of a novel partial premixed bluff body (PPBB) low NO_x burner, capable of operating with hydrogen as well as methane-hydrogen blends, were investigated numerically. The PPBB burner features a frustum shaped conical bluff body generating a flame stabilizing recirculation zone. Fuel is partially premixed via jets in an accelerating cross-flow. Steady-state and transient non-reacting simulations using five different turbulence models, i.e. standard k-ε, realizable k-ε, shear stress transport (SST) k-ω, stress-blended eddy simulation (SBES) and large eddy simulation (LES), were conducted. The simulations were validated against particle image velocimetry (PIV) measurements of an unconfined non-reacting flow. All turbulent models were able to predict the recirculation zone length in good agreement with the experimental data. However, only scale resolving simulations could reproduce velocity magnitudes with sufficient accuracy. Time averaged and instantaneous results from the scale resolving simulation were analysed in order to investigate flow characteristics that are special about the PPBB burner design and of relevance for the combustion process. Two different burner configurations were studied and their effects on the flow field were examined. The recirculation zone volume as well as the entrainment into the wall jet around the bluff body were found to correlate with the elevation of the bluff body relative to the burner throat. Both of these parameters are expected to have a strong impact on the overall NO_x emission, since the near burner region is typically one of the main contributors to the NO_x formation.     

Influence of mass air flow ratio on gas-particle flow characteristics of a swirl burner in a 29 MW pulverized coal boiler

In a gas/particle two-phase test facility, a three-component particle-dynamics anemometer was used to measure the characteristics of gas/particle two-phase flows in a 29 megawatt (MW) pulverized coal industrial boiler equipped with a new type of swirling pulverized coal burner. The distributions of three-dimensional gas/particle velocity, particle volume flux, and particle size distribution were measured under different working conditions. The mean axial velocity and the particle volume flux in the central region of the burner outlet were found to be negative. This indicated that a central recirculation zone was formed in the center of the burner. In the central recirculation zone, the absolute value of the mean axial velocity and the particle volume flux increased when the external secondary air volume increased. The size of the central reflux zone remained stable when the air volume ratio changed. Along the direction of the jet, the peak value formed by the tertiary air gradually moved toward the center of the burner. This tertiary air was mixed with the peak value formed by the air in the adiabatic combustion chamber after the cross-section of x/d = 0.7. Large particles were concentrated near the wall area, and the particle size in the recirculation zone was small.     

燃烧模型在NexGen燃烧器出口流场模拟中的应用

通过求解三维定常雷诺平均的N-S方程,对NexGen燃烧器的出口流场进行数值模拟。首先,利用冷态流场的实验数据验证燃烧器几何模型和数值计算方法的有效性。然后,在计算中分别选取火焰面模型、混合分数PDF模型和涡耗散模型3种燃烧模型,比较燃烧模型对燃烧器出口流场模拟结果的影响。研究结果表明:燃烧模型对Nex Gen燃烧器出口的速度场、火焰形状和热流密度分布基本没有影响,但是对火焰长度、火焰最高温度、最高热流密度及校准面上温度分布和温度值有较大影响。相比火焰面模型和涡耗散模型,混合分数PDF模型的计算结果与实验结果吻合较好,可以为防火试验方案设计提供参考。     

Blowoff mechanism of harmonically forced bluff body stabilized turbulent premixed flames

Flame blowoff under harmonic forcing of upstream mixture velocity is analyzed for bluff-body stabilized conical premixed flames in a laboratory burner. It is found that the forced vortex shedding phenomenon within the recirculation zone, accompanies flame blowoff when the convective wavelength of the imposed oscillation is larger than the recirculation zone length in the streamwise direction. The experimental results obtained from combined particle image velocimetry and planar laser induced fluorescence of OH radical provide evidence for this behavior. The differences between forced and unforced flame blowoff are also discussed.     

钝体燃烧器湍流预混燃烧流动特性的模拟

钝体燃烧器的回流区结构对燃烧具有重要影响,采用经济有效的数学模型对回流区结构进行模拟具有理论价值和实际意义。采用PIV技术测量了一个典型的钝体燃烧器的热态流场,并基于Fluent平台使用3种湍流燃烧速度定义对TFC模型进行求解,分析比较了Zimont、Gulder、Peters和实验得到的流场特性。结果发现Peters的流动特性与实验结果最为接近,都属于射流主导型结构,Peters的进展变量与Zimont和Gulder有明显不同。     

Evolution of soot size distribution in premixed ethylene/air and ethylene/benzene/air flames: Experimental and modeling study

The effect of benzene concentration in the initial fuel on the evolution of soot size distribution in ethylene/air and ethylene/benzene/air flat flames was characterized by experimental measurements and model predictions of size and number concentration within the flames. Experimentally, a scanning mobility particle sizer was used to allow spatially resolved and online measurements of particle concentration and sizes in the nanometer-size range. The model couples a detailed kinetic scheme with a discrete-sectional approach to follow the transition from gas-phase to nascent particles and their coagulation to larger soot particles. The evolution of soot size distribution (experimental and modeled) in pure ethylene and ethylene flames doped with benzene showed a typical nucleation-sized (since particles do not actually nucleate in the classical sense particle inception is often used in place of nucleation) mode close to the burner surface, and a bimodal behavior at greater height above burner (HAB). However, major features were distinguished between the data sets. The growth of nucleation and agglomeration-sized particles was faster for ethylene/benzene/air flames, evidenced by the earlier presence of bimodality in these flames. The most significant changes in size distribution were attributed to an increase in benzene concentration in the initial fuel. However, these changes were more evident for high temperature flames. In agreement with the experimental data, the model also predicted the decrease of nucleation-sized particles in the postflame region for ethylene flames doped with benzene. This behavior was associated with the decrease of soot precursors after the main oxidation zone of the flames.     

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NO_X reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.